The Ukrainian army has reported 11 attacks against its positions in the east where a ceasefire is tentatively holding, and said a drone was spotted over Mariupol, the last major eastern town under its control.

The attacks came as the overall death toll from fighting between government troops and pro-Russian rebels in Ukraine topped 4,600, according to a new UN report.

Ukraine has been worried for months that the Russia-backed separatists would launch an offensive on Mariupol in a bid to build a corridor between the Russian border and the Crimean peninsula, which was annexed by Moscow in March.

The ceasefire introduced on Tuesday was violated 11 times in the past 24 hours, the statement said, with artillery and mortar fire reported at several flashpoints along the line.

"The surveillance activities of the enemy have intensified around Mariupol where a drone was identified," the military said in a statement.

Around the airport in Donetsk - site of some of the fiercest fighting between government and separatist forces in recent months - "the night was rough", a voluntary soldier, Maxim, with the right-wing Pravy Sektor group said.

"Snipers fired on us and explosions were coming from the airport. But everything is calm this morning," he said.

Volodymyr Tiurin, an official in a town in the neighbouring Lugansk province, said all was calm.

"People slept soundly for the fourth night in a row," he said.

More than 1.1 million displaced due to conflict: report

The fighting in eastern Ukraine has claimed more than 4,600 lives and displaced more than a million people, the UN's latest report on the conflict said.

According to the report, about 10,240 people have been wounded since the conflict erupted in April.

More than 1.1 million people have been displaced overall - 542,080 people within Ukraine, the report said.

It said just under 568,000 people fled to neighbouring countries, with the vast majority of those - 465,721 people - to Russia.

Some 5.2 million people live in conflict-afflicted areas, and the report said more than 300 people were killed in less than a month, taking the overall toll to 4,634.

OCHA's last report on the Ukraine crisis on November 20 had put the toll at 4,317.